Look up the Popular Flying Association fly-in. It used to take place ever year and features hundreds of homebuilt aircraft many of which were built in garages by kids and their fathers.
The E A A featured in this video is the Experimental Aircraft Association, the American equivalent of P F A.
It runs a fly-in at Oshkosh in Wisconsin every year and, the last year that I remember being at the P F A equivalent, Oshkosh had more aircraft on the ground than were registered in the UK.